Method of forming shaped hydrogel articles including contact lenses using inert, displaceable diluents

ABSTRACT

Shaped hydrogel articles such as soft contact lenses are prepared by the steps of: 
     (1) molding or casting a polymerization mixture comprising: 
     (a) a monomer mixture comprising a major proportion of one or more hydrophilic monomers such as 2-hydroxyethyl methacrylate, and one or more cross-linking monomers; and 
     (b) an inert, displaceable diluent selected from the group consisting of: 
     (i) ethoxylated alkyl glucoside; 
     (ii) ethoxylated bisphenol A; 
     (iii) polyethylene glycol; 
     (iv) mixture of propoxylated and ethoxylated alkyl glucoside; 
     (v) single phase mixture of ethoxylated or propoxylated alkyl glucoside and C 2-12  dihydric alcohol; 
     (vi) adduct of ε-caprolactone and C 2-6  alkanediols and triols; 
     (vii) ethoxylated C 3-6  alkanetriol; and 
     (viii) mixtures of one or more of (i) through (vii), 
     under conditions to polymerize said monomer mixture to produce a shaped gel of a copolymer of said monomers and said diluent; and 
     (2) thereafter replacing said diluent with water.

This is a division of application Ser. No. 08/096,145, filed Jul. 22 1993, now U.S. Pat. No. 5,457,140 which is hereby incorporated by reference.

The invention relates to the production of shaped hydrogel articles including soft contact lenses, and more particularly to a method for the direct molding of such articles using a new class of inert, displaceable diluents.

BACKGROUND OF THE INVENTION

Until recently, soft contact lenses of the hydrogel type have been manufactured either by lathe cutting or spin casting. In the lathe cutting method, a lens blank or button of a substantially anhydrous hydrophilic polymer (xerogel) is mechanically cut and polished to a lens shape on a fine lathe, and thereafter is contacted with water or saline to hydrate the polymer and form the desired hydrogel lens. The mechanical steps utilized in the lathe cutting operation are similar to those used in the manufacture of hard contact lenses, except that allowance must be made for swelling of the lens during hydration of the polymer.

In the spin casting method, a small quantity of hydrophilic monomer mixture is placed in a concave, optically polished mold, and the mold is rotated while the monomers are polymerized to form a xerogel lens. The two optical surfaces of the lens are formed simultaneously during polymerization, the outer surface being formed by the concave mold surface and the inner surface being shaped by the joint actions of centrifugal force generated by the rotating mold and surface tension of the polymerization mixture. The lens produced thereby is contacted with water or saline to hydrate the polymer and form a hydrogel lens as in the case of the lathe cut lens.

More recently, an improved process for producing hydrogel contact lenses has been developed, which method is not only more economical than either the lathe cut method or the spin casting method, but it has the advantage of enabling a more precise control over the final shape of the hydrated lens. This new method comprises the direct molding of a monomer mixture wherein said mixture is dissolved in a non-aqueous, displaceable solvent, the mixture is placed in a mold having the precise shape of the final desired hydrogel (i. e., water-swollen) lens, and the monomer/solvent mixture is subjected to conditions whereby the monomer(s) polymerize, to thereby produce a polymer/solvent mixture in the shape of the final desired hydrogel lens. (The polymerization is preferably carried out in a non-aqueous medium because water can interfere with the polymerization reaction and adversely affect the properties of the resulting polymer.) After the polymerization is complete, the solvent is displaced with water to produce a hydrated lens whose final size and shape are quite similar to the size and shape of the original molded polymer/solvent article. Such direct molding of hydrogel contact lenses is disclosed in Larsen, U.S. Pat. No. 4,495,313 and in Larsen et al., U.S. Pat. Nos. 4,680,336, 4,889,664 and 5,039,459.

In Larsen, U.S. Pat. No. 4,495,313 and in Larsen et al., U.S. Pat. Nos. 4,889,664 and 5,039,459, the displaceable diluents disclosed are water-displaceable boric acid esters of polyhydric alcohols. In Larsen et al., U.S. Pat. No. 4,680,336, the displaceable diluents disclosed are water-displaceable organic compounds selected on the basis of their viscosity and their Hansen cohesion parameters relative to the cohesion parameters of the polymeric component of the hydrogel to be prepared.

The present invention is based on the discovery of a new class of compositions that can be used as displaceable diluents in the direct molding of shaped hydrogel articles such as soft contact lenses.

BRIEF SUMMARY OF THE INVENTION

Shaped hydrogel articles such as soft contact lenses are prepared by the steps of:

(1) molding or casting a polymerization mixture comprising:

(a) a monomer mixture comprising a major proportion of one or more hydrophilic monomers such as 2 -hydroxyethyl methacrylate, and one or more cross-linking monomers; and

(b) an inert, displaceable non-aqueous diluent selected from the group consisting of:

(i) ethoxylated alkyl glucoside;

(ii) ethoxylated bisphenol A;

(iii) polyethylene glycol;

(iv) mixture of propoxylated and ethoxylated alkyl glucoside;

(v) single phase mixture of ethoxylated or propoxylated alkyl glucoside and dihydric alcohol of up to 12 carbon atoms;

(vi) adduct of ε-caprolactone and C₂₋₆ alkanediols and triols;

(vii) ethoxylated C₃₋₆ alkanetriol; and

(viii) mixtures of one or more of (i) through (vii),

under conditions to polymerize said monomer mixture to produce a shaped gel of a copolymer of said monomers and said diluent; and

(2) thereafter replacing said diluent with water.

THE PRIOR ART

In addition to the Larsen and Larsen et al. patents cited above, other relevant prior art includes the following:

Larsen, U.S. Pat. No. 4,565,348;

Ohkada et al., U.S. Pat. No. 4,347,198;

Shepherd, U.S. Pat. No. 4,208,364;

Mueller et al., EP-A-0 493 320 A2; and

Wichterle et al., Re. 27,401 (U.S. Pat. No. 3,220,960).

DETAILED DESCRIPTION OF THE INVENTION

The inert, displaceable, non-aqueous diluents employed in the process of the invention are selected from the following group:

(i) ethoxylated alkyl glucoside;

(ii) ethoxylated bisphenol A;

(iii) polyethylene glycol;

(iv) mixture of propoxylated and ethoxylated alkyl glucoside;

(v) single phase mixture of ethoxylated or propoxylated alkyl glucoside anddihydric alcohol of up to 12 carbon atoms;

(vi) adduct of ε-caprolactone and C₂₋₆ alkanediols and triols;

(vii) ethoxylated C₃₋₆ alkanetriol; and

(viii) mixtures of one or more of (i) through (vii).

The diluents employed are ultimately water-displaceable. That is, the shaped gel of a copolymer of said monomers and said diluent is treated with a solvent to remove the diluent and ultimately replace it with water.In most cases, the solvent used to remove the inert diluent will be water (or an aqueous solution such as physiological saline). However, if desired, and depending on the solubility characteristics of the inert diluent used in the process of the invention, the solvent initially used to replace the inert diluent can be an organic liquid such as ethanol, methanol, acetone, glycerol, mixtures thereof, or the like, or a mixture of one or more such organic liquids with water, followed by extraction with pure water (or physiological saline) to produce a shaped gel comprising a copolymer of said monomers swollen with water.

Ethoxylated and propoxylated alkyl glucosides are compositions of Formula (I): ##STR1##

wherein R¹ represents a C₁₋₆ alkyl group (preferably methyl), each R individually represents --CH₂ --CH₂ -- or --CH₂ --CH(CH₃)--, and the sum of w, x, y, and z is a number within the range of from about 5 to 50 (preferably from 5 to 30), and represents the total number of ethylene or propylene oxide units in the composition. The diluent represented by Formula (I) can be (i) an ethoxylated alkyl glucoside, (ii) a propoxylated alkyl glucoside, (iii) a mixed ethoxylated/propoxylated alkyl glucoside, or mixture of two or three of (i), (ii), and (iii), provided that a major proportion of the R groups in the mixture of compositions represented by Formula (I) represent --CH₂ --CH₂ -- groups. Ethoxylated and propoxylated alkyl glucosides are commercially available products that are prepared by reacting ethylene oxide or propylene oxide with an alkyl glucoside.

Ethoxylated or propoxylated glucoside can also be employed in a mixture with a dihydric alcohol of up to 12 carbon atoms, and preferably of up to 6 carbon atoms. The mixture of the two materials should be in such proportions that the mixture is single phase. Illustrative dihydric alcohols that can be used include ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, and the like.

Ethoxylated bisphenol A is a compound of Formula (II): ##STR2##

wherein R² represents --CH₂ --CH₂ --, and m+n is a number within the range of from about 2 to about 100 (preferably from about 4 to about 20), and represents the total number of ethylene oxide units in the composition. Ethoxylated bisphenol A is a commercially available product that is prepared by reacting ethylene oxide with bisphenol A.

Polyethylene glycols are compounds that can be represented by Formula (III):

    HO--(CH.sub.2 --CH.sub.2 O).sub.n --H

wherein n represents a number such that the molecular weight of the polyethylene glycol is within the range of from about 300 to about 10,000,and preferably from about 400 to 5000. Such polyethylene glycols are commercially available products.

Adducts of ε-caprolactone with C₂₋₆ alkanediols and triols, are prepared by reacting ε-caprolactone with the C₂₋₆ alkanediol or triol in the presence of a suitable catalyst. Such adducts having molecular weights within the range of from about 300 to about 500 are preferred for use in the invention. Adducts of ε-caprolactone and alkanediols and triols are commercially available products.

Ethoxylated triols such as ethoxylated trimethylolpropane, ethoxylated glycerol, ethoxylated 1,2,6-hexanetriol, and the like can also be used as the inert diluent. The molecular weights of such materials will usually bewithin the range of from about 200 to about 1000.

Mixtures of one or more of the above can also be used in the invention. Preferred examples include mixtures of polyethylene glycol and ethoxylatedbisphenol A, mixtures of polyethylene glycol and ethoxylated alkyl glucoside, mixtures of ethoxylated and/or propoxylated alkyl glucoside with ethoxylated bisphenol A, and mixtures of ethoxylated alkyl glucoside with ethoxylated triols.

The monomer mixture used in the process of the invention contains a major proportion of a hydrophilic monomer such as 2-hydroxyethyl methacrylate ("HEMA") as the major component, one or more cross-linking monomers, and optionally small amounts of other monomers such as methacrylic acid. HEMA is one preferred hydrophilic monomer. Other hydrophilic monomers that can be employed include 2-hydroxyethyl acrylate, 2-hydroxypropyl methacrylate,2-hydroxypropyl acrylate, 3-hydroxypropyl methacrylate, N-vinyl pyrrolidone, glycerol mono-methacrylate, glycerol mono-acrylate, and the like.

Other hydrophilic monomers that can be employed in the invention include polyoxyethylene polyols having one or more of the terminal hydroxyl groupsreplaced with a functional group containing a polymerizable double bond. Examples include polyethylene glycol, ethoxylated alkyl glucoside, and ethoxylated bisphenol A reacted with one or more molar equivalents of an end-capping group such as isocyanatoethyl methacrylate ("IEM"), methacrylic anhydride, methacroyl chloride, vinylbenzoyl chloride, or the like, to produce a polyethylene polyol having one or more terminal polymerizable olefinic groups bonded to the polyethylene polyol through linking moieties such as carbamate or ester groups. The Examples below include several representative preparations of such "end-capped" polyoxyethylene polyols.

The cross-linking monomers that can be employed, either singly or in combination, include ethylene glycol dimethacrylate ("EGDMA"), trimethylolpropane trimethacrylate ("TMPTMA"), glycerol trimethacrylate, polyethylene glycol dimethacrylate (wherein the polyethylene glycol has a molecular weight up to, e. g., about 5000), and other polyacrylate and polymethacrylate esters, such as the end-capped polyoxyethylene polyols described above containing two or more terminal methacrylate moieties. Thecross-linking monomer is used in the usual amounts, e.g., from about 0.000415 to about 0.0156 mol per 100 grams of reactive monomer mixture. The cross-linking monomer can be a hydrophilic monomer.

Other monomers that can be used include methacrylic acid, which is used to influence the amount of water that the hydrogel will absorb at equilibrium. Methacrylic acid is usually employed in amounts of from about0.2 to about 8 parts, by weight, per 100 parts of hydrophilic monomer. Other monomers that can be present in the polymerization mixture include methoxyethyl methacrylate, acrylic acid, ultra-violet absorbing monomers, and the like.

A polymerization catalyst is included in the monomer mixture. The polymerization catalyst can be a compound such as lauroyl peroxide, benzoyl peroxide, isopropyl percarbonate, azobisisobutyronitrile, or the like, that generates free radicals at moderately elevated temperatures, orthe polymerization catalyst can be a photoinitiator system such as an aromatic α-hydroxy ketone or a tertiary amine plus a diketone. Illustrative examples of photoinitiator systems are 2-hydroxy-2-methyl-1-phenyl-propan-1-one and a combination of camphorquinone and ethyl 4-(N,N-dimethylamino)benzoate. The catalyst is used in the polymerization reaction mixture in catalytically effective amounts, e.g., from about 0.1 to about 2 parts by weight per 100 parts of hydrophilic monomer such as HEMA.

The Examples below illustrate the practice of the invention. Some of the materials that are employed in the Examples are identified as follows:

Ethoxylated Bisphenol A (ethoxylated 2,2-bis (4-hydroxyphenyl)propane)--"Photonol 7025" [m+n in Formula (II)=8] and "Photonol 7028" (m+n in Formula (II)=4);

Ethoxylated trimethylolpropane--"Photonol 7158" (m.w.=730);

4-Methoxyphenol (hydroquinone monomethyl ether)--"MEHQ";

Isocyanatoethyl methacrylate--"IEM";

N,N-dimethylacrylamide--"DMA";

Polyethylene glycol--"PEG nnnn" wherein the "nnnn" refers to the molecular weight;

Ethoxylated (or propoxylated) methyl glucoside--"GLUCAM's E-5, P-10, E-10 and (E-20"--["E-5" signifies a total of 5 ethylene oxide units added to methyl glucoside, "P-10" signifies a total of 10 propylene oxide units added to methyl glucoside, etc.);

Isophoronediisocyanate(5-isocyanato-1-(isocyanatomethyl)-1,3,3,-trimethylcyclohexane)--"IPDI";

Polyethylene glycol nnn boric acid ester--"PEG nnn BAE";

1,4-Butanediol boric acid ester--"1,4-BDBAE";

Hydroxyethyl methacrylate--"HEMA";

Methacrylic acid--"MAA";

Ethylene glycol dimethacrylate--"EGDMA";

Trimethylolpropane trimethacrylate--"TMPTMA";

2-hydroxy-2-methyl-1-phenyl-propan-1-one--"DAROCURE 1173";

Polycaprolactone triol=reaction product (ester) of ε-caprolactone with glycerol, m.w. about 300 --"PCLT300";

1,2,6-trihydroxyhexane--"1,2,6-THH";

Diethylene glycol--"DEG";

Ethylene glycol--"EG";

1,4-Butane diol--"1,4-BuDiol";

1,4-Butane diol/boric acid ester--"1,4-BDBAE"

1,2-Propane diol--"1,2-ProDiol";

Boric acid/glycerol ester--"BAGE"

TEST METHODS

The following test methods are employed in the Examples:

Test Method 1: PhotoDSC Determinations

All photocalorimetric measurements were carried out on a DuPont DSC model 910 unit equipped with an 830 photocalorimeter attachment and Omnitherm software. Sample size was 4.5-6.0 mg in every case. Operating conditions were as follows: temperature 45° C., N₂ atmosphere (10 min purge at 40 mL/min prior to irradiation), intensity of the UV lamp source was 2.5-3.0 mW/cm².

Maximum polymerization rates (R_(p) ^(max)) were calculated from the following equation:

    R.sub.p.sup.max =(M).sub.o /Q.sub.∞) (dQ/dt).sub.max (1)

where Q.sub.∞ and (M)_(o) denote the total heat evolved by the sample and the methacrylate double bond concentration, respectively, and (dQ/dt)_(max) is the maximum rate of heat evolution observed (at t=T_(max)) (T_(max) =time to peak exotherm, which coincides with the time at which the polymerization reaches its maximum rate of reaction). Note that Q.sub.∞ is obtained from the DSC trace by integrating the area under the exotherm (total heat evolved per sample unit mass, i.e. Q_(m)) and multiplying this quantity by the sample mass. (M)_(o) is obtained by simply calculating the double bond concentration in the formulation, including diluent. The density of the RMM ("Reactive Monomer Mixture") needs to be determined in order to calculate (M)_(o) in moles of methacrylate group per unit volume of RMM.

It has been found that T_(max) will normally be within the range of from about 0.2 to about 3.5 minutes, and preferably from about 0.4 to about 2.5minutes, for those inert, displaceable diluents that can be employed successfully in the particular reactive monomer mixture employed. Therefore, a convenient test to determine whether any proposed inert, displaceable diluent can be employed with any given reactive monomer mixture to produce a shaped gel (any shape will do--it need not be in the shape of a contact lens for the test) of a copolymer of said monomers thatis useful for use as a contact lens, is to determine the T_(max) by the PhotoDSC test given above. The useful inert, displaceable diluents for that particular RMM will yield a T_(max) within the ranges given above.

It has also been found that, in most cases, a % conversion of the reactive monomer mix (as determined by dividing the area under the DSC trace up to T_(max) by the total area under the DSC trace), in the Photo DSC test given above, of at least 40% at T_(max), and preferably at least 50%, isrequired in order to produce an optically clear gel.

Test Method 2: RMM and Diluent Density Measurements

All liquid densities were measured by a method based on Archimedes principle. A Sartorius Research balance fitted with a liquid density kit (available from the manufacturer) was used to carry out all measurements. The method consists in weighing a glass bob in and out of the liquid beingtested. The volume of the glass bob is predetermined using a liquid of known density (e.g. water).

The densities of high viscosity liquids (e.g. boric acid esters) were determined with the use of an aluminum pycnometer whose volume had been measured using deionized water at a given temperature.

Test Method 3. Tensile Properties (Modulus, Elongation and Strength)

The lens to be tested is cut to the desired specimen size and shape, and the cross sectional area measured. The sample is then attached into the upper grip of a crosshead movement type of testing instrument equipped with a load cell. The crosshead is lowered to the initial gauge length andthe sample specimen attached to the fixed grip. The sample is then elongated at a constant rate of strain and the resulting stress-strain curve is recorded. The elongation is expressed in percent and the tensile modulus and strength is expressed in psi (lbs/in²). It has been foundthat for a shaped gel to be useful as a contact lens, the modulus of the shaped gel should be at least about 20 psi, and preferably at least about 25 psi.

Test Method 4. Gravimetric Water Content

Samples for gravimetric water content measurements were prepared as follows:

A number of 20 mm diameter×3 mm deep cylindrical polystyrene cavitieswere hand filled with degassed HEMA-based formulations and cured for approximately 20 minutes under fluorescent tubes in a N₂ atmosphere. The total measured energy dose was 1.2-1.6 Joules/cm². The polymer/diluent disks were demolded from the polystyrene cavities using a hot plate. The disk were then cut with a no.7 cork bore to obtain a 9-10 mm diameter disk. Typically, the polystyrene cavities are filled with sufficient reactive monomer mix to obtain a 1-1.5 mm thick disk. The diluent swollen polymer disks are hydrated in deionized water for 3 hrs at70° C., and subsequently allowed to remain for an additional 3 days at room temperature. The disks are then removed from the DI (de-ionized) water bath, air dried for 10-15 hrs, and subsequently Vacuum dried (<1.5 mm Hg) at 100° C. for 2 hrs. The weight of each disk is taken, and the disk are then placed in physiological saline for 2 days. The polymer disks are then removed from the saline solution, blotted carefully to remove surface water, and weighed again. The water content is then calculated as follows:

    % Water=100 (m.sub.wet -m.sub.dry)/m.sub.wet               (2)

Where m_(dry) and m_(wet) denote the weight of the polymer disks beforeand after hydration, respectively.

Test Method 5. Oxygen Permeability (Dk)

The oxygen permeability was measured by the method of Fatt et al., "Measurement of Oxygen Transmissibility and Permeability of Hydrogel Lenses and Materials", International Contact Lens Clinic, Vol. 9/No.2, March/April 1982, p 76. A polarographic oxygen sensor consisting of a 4 mmdiameter gold cathode and a silver-silver chloride ring anode is used in this method. The measured oxygen permeability is denoted by Dk, where D represents the diffusion coefficient for oxygen in the material being tested, and k is the solubility of oxygen in the material. The permeability (Dk) units are (cm² /s)(mL O₂ /mL·mm Hg).

The following six examples illustrate the preparation of reactive cross-linkers (Examples 1-4), and two prior art diluents (Examples 5 and 6):

EXAMPLE 1 Synthesis of dicapped ethoxylated Bisphenol A (BPA 890)

To a 5 L three neck round bottom flask are added 728 g (1.255 mol) of driedPhotonol 7025 (molecular weight=580 g/mol), 1.5 L of dry acetonitrile, 1.0 g of 4-methoxy phenol (MEHQ) and 0.5 g of stannous octoate (approximately 0.1 mol % relative to diol). After these components are added, the resulting solution is purged with dry O₂ for 30-45 minutes (a gas diffuser is used for this purpose). After the O₂ purge is completed, 365 g (2.35 mol) of isocyanatoethyl methacrylate (IEM) and 730 g of acetonitrile are charged to a 1 L addition funnel (this operation is preferably carried out under N₂).

The contents of the addition funnel (i.e. the IEM solution) are then added,dropwise with vigorous stirring, to the 5 L round bottom flask. The addition should take about 2-3 hours to complete. After the IEM addition is complete, the addition funnel is rinsed with 50-100 mL of acetonitrile.The progress of the reaction is followed monitored by following the disappearance of the NCO absorption at 2270 cm⁻¹ in the infrared spectra. The acetonitrile is removed under reduced pressure and the resultant viscous liquid dicapped bisphenol A 890 is used as prepared.

EXAMPLE 2 Synthesis of dicapped polyethylene glycol (PEG) 4000

A total of 200 g (0.05 mol) of dry PEG 4000 is placed into a 1 L three neckround bottom flask equipped with mechanical agitation, and a gas-inlet tube. A dry nitrogen blanket is established in the reaction vessel. To this flask is added 375 g of dry acetonitrile and the PEG 4000 is allowed to sit until it has completely dissolved. Subsequently, two drops of stannous octoate and 500 ppm of MEHQ are added. To a 100 mL addition funnel are added 15.52 g (0.100 mol) of IEM and 50 mL of acetonitrile. After the addition of the IEM is completed, the reaction progress is monitored by following the disappearance of the NCO absorption at 2270⁻¹ in the infrared spectra. After the reaction is completed, the acetonitrile is removed under reduced pressure and the resultant white waxy dicapped PEG 4000 is used as is.

EXAMPLE 3 Synthesis of dicapped polyethylene glycol (PEG) 4500

A total of 22534 g (0.05 mol) of dry PEG 4500 is placed into a 1 L three neck round bottom flask equipped with mechanical agitation and a gas inlet-tube. The system is flushed successively with dry nitrogen and dry oxygen. To this flask are added 375 g of dry acetonitrile and the PEG 4500is allowed to sit until it has completely dissolved. Subsequently, 2 drops of stannous octoate and 500 ppm MEHQ are added. To a 100 mL addition funnel are added 15.52 g (0.100 mol) of IEM, and 50 mL of acetonitrile. After addition of the IEM is completed, the reaction progress is monitoredby following the disappearance of the NCO absorption at 2270 cm⁻¹. After the reaction is completed, the acetonitrile is removed under reducedpressure and the resultant white waxy dicapped PEG 4500 is used as is.

EXAMPLE 4 Synthesis of GLUCAM E-20/polyethylene glycol (PEG) 4500 Derivative

A total of 100 g of dry PEG 4500 (0.022 mol) is placed into a three neck. 1L round bottom flask equipped with mechanical agitation and a gas-inlet tube. The system is then flushed successively with dry nitrogen and dry oxygen. To this flask is then added 375 g of dry acetonitrile and the PEG 4500 is allowed to sit until it has completely dissolved. Subsequently, 2 drops of stannous octoate and 500 ppm of MEHQ are added. To an addition funnel are added 3.41 g (0.022 mol) of IEM and 10 mL of acetonitrile. After the addition of the IEM is completed, the reaction progress is followed by monitoring the disappearance of the NCO absorption at 2270 cm⁻¹ in the infrared spectra. When this peak has completely disappeared, the above reaction mixture is transferred to a 500 mL addition funnel. The contents of the addition funnel are slowly added to athree necked round bottom 2 L flask containing a solution of 200 g of dry acetonitrile and 4.89 g (0.022 mol) of isophorone diisocyanate (IPDI). Provisions should be made for efficient mechanical agitation throughout the addition. After the addition is completed, the reaction is followed bymonitoring the disappearance of the PEG hydroxyl peak centered at 3400 cm⁻¹ in the infrared spectrum. To the above mixture are then added 6.0 g (0.006 mol) of GLUCAM E-20 in 50 mL of acetonitrile. After the NCO absorption at 2270 cm⁻¹ has disappeared, the acetonitrile is removed under reduced pressure and the resultant white powder GLUCAME-20/PEG 4500 solid is used as is.

EXAMPLE 5 Synthesis of PEG 400 Boric Acid Ester Diluent (PEG 400 BAE)

A total of 400 g (1 mol) of polyethylene glycol 400 (PEG 400) is placed into a 2 L rotary evaporator flask. To this flask are added 123.7 g (2.0 mols) of boric acid. The flask is placed on a rotary evaporator and the pressure is slowly reduced to 0.5-1.0 mm Hg. After full vacuum is established, the temperature of the bath is slowly raised to 92° C.Water is recovered from the reaction as the boric acid ester is formed. Theclear viscous liquid PEG 400 BAE is used as is. [This diluent is illustrative of the prior art diluents disclosed by Larsen et al., U.S. Pat. Nos. 5,039,459 and 4,889,664.]

EXAMPLE 6 Synthesis of 1,4-Butanediol Boric Acid Ester (1,4-BDBAE)

A total of 277.7 g (4.5 mols) of boric acid was placed into a 3 L rotary evaporator flask. To this flask was added 1,223 g of 1,4-butanediol (13.6 mols). The flask is then placed on a rotary evaporator and the pressure isslowly reduced to 0.5-1.0 mm Hg. After full vacuum is established, the temperature of the bath is slowly raised to 85° C. at approximately5° C. per 20 minutes. Water is recovered from the reaction as the boric acid ester is formed. The clear viscous liquid 1,4-BDBAE is used as is. (This diluent is illustrative of the prior art diluents disclosed by Larsen et al., U.S. Pat. Nos. 5,039,459 and 4,889,664.)

EXAMPLES 7-35

In these examples, various diluents were employed to prepare soft contact lenses from the following reactive monomer mixture:

A blend is prepared using 96.8% by weight of HEMA, 1.97% methacrylic acid, 0.78% ethylene glycol dimethacrylate (EGDMA), 0.1% of trimethylolpropane trimethacrylate (TMPTMA) and 0.34% of DAROCUR 1173. To this monomer mix isadded the inert, displaceable diluent being evaluated. After thoroughly mixing the formulation at ambient temperature, the mixture is allowed to stir under reduced pressure (40 mm Hg) for 30 min (at 25° C.) and subsequently transferred to contact lens molds. The filled molds are exposed to UV light (wavelength=300-380 nm, dose=1.2-1.6 Joules/cm₂) for 20 minutes at approximately 50° C. The molds are then separated, and placed in physiological saline for 3.0 hrs at 70° C.to remove the inert diluent and any residual unreacted monomers. After thisinitial hydration period the lenses are allowed to equilibrate to room temperature in a fresh bath of physiological saline. The lenses are then tested according to Test Methods 3, 4 and 5.

The Tables below display the diluents evaluated, the monomer/diluent ratios, and the results of the tests made in accordance with Test Methods 3, 4 and 5, for Examples 7-35:

    ______________________________________                                                     Example 7  Example 8  Example 9                                    ______________________________________                                         Composition (%):                                                               HEMA        96.8       96.8       96.8                                         MAA         1.97       1.97       1.97                                         EGDMA       0.78       0.78       0.78                                         TMPTMA      0.1        0.1        0.1                                          Darocur 1173                                                                               0.34       0.34       0.34                                         Diluent:    GLUCAM     GLUCAM     GLUCAM                                                   E20        E10        E5                                           Mon./Dil. Ratio                                                                            48:52      48:52      48:52                                        Properties:                                                                    Modulus (psi)                                                                              34 ± 4  36 ± 3  33 ± 4                                    % Elongation                                                                               149 ± 50                                                                               148 ± 63                                                                               174 ± 46                                  Tens. Strength                                                                              40 ± 10                                                                                40 ± 12                                                                               46 ± 9                                    (psi)                                                                          Water Content (%)                                                                          57.4 ± .7                                                                              54.4 ± .2                                                                              59.9 ± .3                                 Hydrogel    Clear      Clear      Clear                                        Kinetic Parameters:                                                            Tmax (min)  1.75       1.65       1.48                                         Conv. @ Tmax (%)                                                                           64.5       64.7       61.4                                         ______________________________________                                                     Example 10 Example 11                                                          Control    Control                                                             (Prior art)                                                                               (Prior art)                                                                               Example 12                                   ______________________________________                                         Composition (%):                                                               HEMA        96.8       96.8       96.8                                         MAA         1.97       1.97       1.97                                         EGDMA       0.78       0.78       0.78                                         TMPTMA      0.1        0.1        0.1                                          Darocur 1173                                                                               0.34       0.34       0.34                                         Diluent:    1,2,6-THH   Glycerol  Phot 7158                                    Mon./Dil. Ratio                                                                            48:52      48:52      48:52                                        Properties:                                                                    Modulus (psi)                                                                              25 ± 2  40 ± 3  27 ± 2                                    % Elongation                                                                               183 ± 53                                                                               119 ± 33                                                                               174 ± 49                                  Tens. Strength                                                                              36 ± 80                                                                                37 ± 72                                                                               37 ± 7                                    (psi)                                                                          Water Content (%)                                                                          59.9 ± .1                                                                              60.6 ± .6                                                                              59.5 ± .3                                 Hydrogel    Clear      Clear      Clear                                        Kinetic Parameters:                                                            Tmax (min)  1.80       1.53       2.15                                         Conv. @ Tmax (%)                                                                           73.4       70.9       65.1                                         ______________________________________                                                     Example 13 Example 14 Example 15                                   ______________________________________                                         Composition (%):                                                               HEMA        96.8       96.8       96.8                                         MAA         1.97       1.97       1.97                                         EGDMA       0.78       0.78       0.78                                         TMPTMA      0.1        0.1        0.1                                          Darocur 1173                                                                               0.34       0.34       0.34                                         Diluent:    Phot 7025  Phot 7028  PCLT300                                      Mon./Dil. Ratio                                                                            48:52      48:52      48:52                                        Properties:                                                                    Modulus (psi)                                                                              33 ± 3  34 ± 3  29 ± 3                                    % Elongation                                                                               200 ± 76                                                                               191 ± 48                                                                               179 ± 55                                  Tens. Strength                                                                              48 ± 15                                                                               47 ± 9  40 ± 9                                    (psi)                                                                          Water Content (%)                                                                          62.2 ± .2                                                                              59.3 ± .5                                                                              61.0 ± .6                                 Hydrogel    Clear      Clear      Clear                                        Kinetic Parameters:                                                            Tmax (min)  1.52       1.47       1.72                                         Conv. @ Tmax (%)                                                                           62.2       61.2       69.0                                         ______________________________________                                                                           Example 18                                               Example 16 Example 17 Control                                                  Control    Control    (Prior                                                   (Prior art)                                                                               (Opaque)   art)                                         ______________________________________                                         Composition (%):                                                               HEMA        96.8       96.8       96.8                                         MAA         1.97       1.97       1.97                                         EGDMA       0.78       0.78       0.78                                         TMPTMA      0.1        0.1        0.1                                          Darocur 1173                                                                               0.34       0.34       0.34                                         Diluent:    1,4-BDBAE  GLUCAM     DEG                                                                 P10                                                     Mon./Dil. Ratio                                                                            48:52      48:52      48:52                                        Properties:                                                                    Modulus (psi)                                                                              27 ± 2  16 ± 4  14 ± 3                                    % Elongation                                                                               124 ± 20                                                                               266 ± 35                                                                               203 ± 56                                  Tens. Strength                                                                              28 ± 35                                                                                48 ± 12                                                                               25 ± 4                                    (psi)                                                                          Water Content (%)                                                                          62.6 ± .6                                                                              63.5 ± .5                                                                              65.4 ± .8                                 Hydrogel    Clear      Opaque     Clear                                        Kinetic Parameters:                                                            Tmax (min)  1.08       0.87       4.83                                         Conv. @ Tmax (%)                                                                           59.5       31.5       83.3                                         ______________________________________                                                     Example 19 Example 20                                                          Control    Control                                                             (Prior art)                                                                               (Prior art)                                                                               Example 21                                   ______________________________________                                         Composition (%):                                                               HEMA        96.8       96.8       96.8                                         MAA         1.97       1.97       1.97                                         EGDMA       0.78       0.78       0.78                                         TMPTMA      0.1        0.1        0.1                                          Darocur 1173                                                                               0.34       0.34       0.34                                         Diluent:    PEG        BAGE       PEG 400                                                  400BAE                                                             Mon./Dil. Ratio                                                                            48:52      48:52      48:52                                        Properties:                                                                    Modulus (psi)                                                                              33 ± 2  34 ± 2  25 ± 3                                    % Elongation                                                                               134 ± 29                                                                               114 ± 42                                                                               179 ± 35                                  Tens. Strength                                                                             35 ± 5  34 ± 8  19 ± 2                                    (psi)                                                                          Water Content (%)                                                                          60.4 ± .2                                                                              62.7 ± .3                                                                              62.7 ± .8                                 Hydrogel    Clear      Clear      Clear                                        Kinetic Parameters:                                                            Tmax (min)  0.52       1.37       3.61                                         Conv. @ Tmax (%)                                                                           34.8       68.8       68.9                                         ______________________________________                                                                           Example 24                                               Example 22 Example 23 Control                                                  (Low       Control    (Prior                                                   modulus)   (Prior art)                                                                               art)                                         ______________________________________                                         Composition (%):                                                               HEMA        96.8       96.8       96.8                                         MAA         1.97       1.97       1.97                                         EGDMA       0.78       0.78       0.78                                         TMPTMA      0.1        0.1        0.1                                          Darocur 1173                                                                               0.34       0.34       0.34                                         Diluent:    1,4-BuDiol 1,2-ProDiol                                                                               EG                                           Mon./Dil. Ratio                                                                            48:52      48:52      48:52                                        Properties:                                                                    Modulus (psi)                                                                              13 ± 1  16 ± 1  23 ± 2                                    % Elongation                                                                               215 ± 66                                                                               215 ± 53                                                                               168 ± 30                                  Tens. Strength                                                                             23 ± 6  28 ± 6  27 ± 4                                    (psi)                                                                          Water Content (%)                                                                          66.4 ± .6                                                                              --         59.9 ± .2                                 Hydrogel    Clear      Clear      Clear                                        Kinetic Parameters:                                                            Tmax (min)  3.42       5.48       4.80                                         Conv. @ Tmax (%)                                                                           65.4       71.5       75.0                                         ______________________________________                                                     Example 25 Example 26 Example 27                                               Control    Control    Control                                                  (Opaque)   (Opaque)   (Opaque)                                     ______________________________________                                         Composition (%):                                                               HEMA        96.8       96.8       96.8                                         MAA         1.97       1.97       1.97                                         EGDMA       0.78       0.78       0.78                                         TMPTMA      0.1        0.1        0.1                                          Darocur 1173                                                                               0.34       0.34       0.34                                         Diluent (%):                                                                   GLUCAM P-10 95         85         70                                           GLUCAM E-10 5          15         30                                           Mon./Dil. Ratio                                                                            48:52      48:52      48:52                                        Properties:                                                                    Modulus (psi)                                                                              12 ± 1  17 ± 2  21 ± 2                                    % Elongation                                                                               282 ± 56                                                                               233 ±  45                                                                              192 ± 42                                  Tens. Str. (psi)                                                                           43 ± 9  44 ± 8  40 ± 11                                   Water Content (%)                                                                          68.7 ± .4                                                                              69.8 ± .6                                                                              68.9 ± .4                                 Hydrogel    Opaque     Opaque     Opaque                                       Kinetic Parameters:                                                            Tmax (min)  0.85       0.98       1.14                                         Conv. @ Tmax (%)                                                                           28.8       38.5       49.1                                         ______________________________________                                                     Example 28 Example 29                                              ______________________________________                                         Composition (%):                                                               HEMA        96.8       96.8                                                    MAA         1.97       1.97                                                    EGDMA       0.78       0.78                                                    TMPTMA      0.1        0.1                                                     Darocur 1173                                                                               0.34       0.34                                                    Diluent (%):                                                                   GLUCAM P-10 40         20                                                      GLUCAM E-10 60         80                                                      Mon./Dil. Ratio                                                                            48:52      48:52                                                   Properties:                                                                    Modulus (psi)                                                                              38 ± 3  38 ± 4                                               % Elongation                                                                               162 ± 32                                                                               199 ± 55                                             Tens. Strength                                                                             44 ± 9   49 ± 11                                             (psi)                                                                          Water Content (%)                                                                          59.5 ± .2                                                                              58.4 ± .5                                            Hydrogel    Clear      Clear                                                   Kinetic Parameters:                                                            Tmax (min)  1.47       1.56                                                    Conv. @ Tmax (%)                                                                           62.2       64.1                                                    ______________________________________                                                     Example 30 Example 31                                                          Control    Control                                                             (Opaque)   (Opaque)   Example 32                                   ______________________________________                                         Composition (%):                                                               HEMA        96.8       96.8       96.8                                         MAA         1.97       1.97       1.97                                         EGDMA       0.78       0.78       0.78                                         TMPTMA      0.1        0.1        0.1                                          Darocur 1173                                                                               0.34       0.34       0.34                                         Diluent (%):                                                                   GLUCAM P-10 95         85         70                                           1,4-BuDiol  5          15         30                                           Mon./Dil. Ratio                                                                            48:52      48:52      48:52                                        Properties:                                                                    Modulus (psi)                                                                              14 ± 1  21 ± 3  25 ± 4                                    % Elongation                                                                               209 ± 49                                                                               194 ± 43                                                                               175 ± 59                                  Tens. Str. (psi)                                                                           35 ± 9   41 ± 10                                                                                31 ± 10                                  Water Content (%)                                                                          69.3 ± .6                                                                              70.1 ± .3                                                                              62.2 ± .3                                 Hydrogel    Opaque     Opaque     Clear                                        Kinetic Parameters:                                                            Tmax (min)  0.96       1.21       2.24                                         Conv. @ Tmax (%)                                                                           37.5       51.6       66.2                                         ______________________________________                                                     Example 33 Example 34 Example 35                                               (Modulus   (Modulus   (Modulus                                                 borderline)                                                                               borderline)                                                                               borderline)                                  ______________________________________                                         Composition (%):                                                               HEMA        96.8       96.8       96.8                                         MAA         1.97       1.97       1.97                                         EGDMA       0.78       0.78       0.78                                         TMPTHA      0.1        0.1        0.1                                          Darocur 1173                                                                               0.34       0.34       0.34                                         Diluent (%):                                                                   GLUCAM P-10 50         40         20                                           1,4-BuDiol  50         60         80                                           Mon./Dil. Ratio                                                                            48:52      48:52      48:52                                        Properties:                                                                    Modulus (psi)                                                                              20 ± 3  21 ± 2  19 ± 1                                    % Elongation                                                                               160 ± 41                                                                               201 ± 63                                                                               258 ± 80                                  Tens. Str. (psi)                                                                           23 ± 7   31 ± 60                                                                                36 ± 90                                  Water Content (%)                                                                          62.2 ± .3                                                                              62.4 ± .4                                                                              62.9 ± .1                                 Hydrogel    Clear      Clear      Clear                                        Kinetic Parameters:                                                            Tmax (min)  2.81       3.23       3.43                                         Conv. @ Tmax (%)                                                                           69.4       68.9       60.2                                         ______________________________________                                    

EXAMPLES 36-39

In these examples, Photonol 7025 was employed as the diluent in conjunctionwith a reactive monomer mix containing HEMA, the reactive cross-linker of Example 4, and Darocur 1173, in various proportions. The following is an illustrative preparation: A monomer mixture containing of 25% by weight ofthe PEG 4500-GLUCAM E-20 derivative described in Example 4, 0.35% DAROCUR 1173, and 74.7% of HEMA was mixed With Photonol 7025, an inert, displaceable diluent in such-amounts as to make up a 48% monomer, 52% diluent blend. After thoroughly mixing the above formulation at 65°C., the mixture is allowed to stir under reduced pressure (40 mm Hg) for 30min (at 65° C.) and subsequently transferred to contact lens molds. The filled molds are exposed to UV light (wavelength =300-380 nm, dose=1.2-1.6 Joules/cm₂) for 20 minutes at approximately 65° C. The molds are then separated, and placed in physiological saline for 3.0 hrs at 70° C. to remove the inert diluent and any residual unreacted monomers. After this initial hydration period the lenses are allowed to equilibrate to room temperature in a fresh bath of physiological saline. The lenses are then tested according to Test Methods3, 4 and 5.

The following table displays the proportions used in the reactive monomer mixtures and the results of the tests made in accordance with Test Methods3, 4 and 5 for Examples 36-39:

    ______________________________________                                                   Example                                                                               Example   Example  Example                                              36     37        38       39                                                   (Modulus                                                                              (Modulus  (Modulus (Modulus                                             border-                                                                               border-   border-  border-                                              line)  line)     line)    line)                                      ______________________________________                                         Composition (%)                                                                HEMA        74.7     64.7      49.7   39.7                                     PEG4500-GLUE20                                                                             25       35        50     60                                       Darocur 1173                                                                               0.35     0.35      0.35   0.35                                     Diluent:    Pho 7025 Pho 7025  Pho 7025                                                                              Pho 7025                                 Mon./Dil. Ratio                                                                            48:52    48:52     48:52  48:52                                    Properties:                                                                    Modulus (psi)                                                                              22 ± 1                                                                               19 ± 1 22 ± 8                                                                             20 ± 3                                % Elongation                                                                               266 ± 42                                                                             218 ± 44                                                                              180 ± 76                                                                           160 ± 41                              Tens. Str. (psi)                                                                           35 ± 5                                                                               30 ± 5 15 ± 2                                                                             23 ± 7                                Water Content (%)                                                                          55 ± 2                                                                               69 ± 1 70 ± 1                                                                             80 ± 2                                Hydrogel    Clear    Clear     Clear  Clear                                    Dk          31.5     40.3      60.5   41.3                                     ______________________________________                                    

EXAMPLES 40-44

In these examples, Photonol 7025 was used as the diluent in conjunction with a reactive monomer mixture of HEMA, MAA, PEG 4500XL (Example 3), BPA890XL (Example 1), and Darocur 1173, in various proportions. The following is an illustrative preparation:

A reactive monomer blend made up of 5.78% by weight of the PEG 4500 cross-linker described in Example 3, 11.1% of the ethoxylated bisphenol A cross-linker described in Example 1, 0.34% DAROCUR 1173, 1.98% methacrylicacid, and 80.8% HEMA was mixed with enough Photonol 7025 to make up a 48% monomer mix and 52% diluent. After thoroughly mixing the above blend at 65° C., the mixture is allowed to stir under reduced pressure (40 mm Hg) for 30 min (at 65° C.) and subsequently transferred to contact lens molds. The filled molds are exposed to UV light (wavelength=300-380 nm, dose=1.2-1.6 Joules/cm₂) for 20 minutes at approximately 65° C. The molds are then separated, and placed in physiological saline for 3.0 hrs at 70° C. to remove the inert diluent and any residual unreacted monomers. After this initial hydration period the lenses are allowed to equilibrate to room temperature in a fresh bath of physiological saline. The lenses are then tested according to Test Methods 3, 4 and 5.

The following table displays the proportions of the monomers and the results of the tests made in accordance with Test Methods 3, 4 and 5 for Examples 40-44:

    ______________________________________                                                     Example 40 Example 41 Example 42                                   ______________________________________                                         Composition (%):                                                               HEMA        80.8       75.3       64.5                                         MAA         1.98       1.98       1.98                                         PEG 4500XL  5.78       11.1       22.1                                         BPA890XL    11.1       11.1       11.1                                         Darocur 1173                                                                               0.34       0.34       0.34                                         Diluent:    Phot 7025  Phot 7025  Phot 7025                                    Mon./Dil. Ratio                                                                            48:52      48:52      48:52                                        Properties:                                                                    Modulus (psi)                                                                              68 ± 6  84 ± 9  80 ± 9                                    % Elongation                                                                                57 ± 16                                                                                59 ± 13                                                                                90 ± 27                                  Tens. Strength                                                                              48 ± 12                                                                               51 ± 9   76 ± 19                                  (psi)                                                                          Water Content (%)                                                                          36 ± 1  41 ± 1  52 ± 1                                    Hydrogel    Clear      Clear      Clear                                        Dk          20.5       23.0       28.8                                         ______________________________________                                                     Example 43 Example 44                                              ______________________________________                                         Composition (%):                                                               HEMA        53.9       41.9                                                    MAA         1.98       1.98                                                    PEG 4500XL  32.7       44.7                                                    BPA890XL    11.1       11.1                                                    Darocur 1173                                                                               0.34       0.34                                                    Diluent:    Phot 7025  Phot 7025                                               Mon./Dil. Ratio                                                                            48:52      48:52                                                   Properties:                                                                    Modulus (psi)                                                                              84 ± 8  81 ± 9                                               % Elongation                                                                                84 ± 22                                                                                80 ± 32                                             Tens. Strength                                                                              73 ± 16                                                                                78 ± 34                                             (psi)                                                                          Water Content (%)                                                                          59 ± 1  63 ± 1                                               Hydrogel    Clear      Clear                                                   Dk          35.7       39.7                                                    ______________________________________                                    

EXAMPLES 45-59

In these examples, Photonol 7025 was used as the diluent in conjunction with a reactive monomer mixture of HEMA, MAA, PEG 4000XL (Example 2), diglycidyl bisphenol A dimethacrylate (Example 1), and Darocur 1173, in various proportions. The following is an illustrative preparation:

A reactive monomer blend made up of 90.6% by weight of HEMA, 1.98% by weight of MAA, 5% by weight of the PEG 4000XL cross-linker described in Example 2, 2.04% by weight of the diglycidyl bisphenol A dimethacrylate cross-linker of Example 1, and 0.34% DAROCUR 1173, was mixed with enough Photonol 7025 to make up a 48% monomer mix and 52% diluent. After thoroughly mixing the above blend at 65° C., the mixture is allowedto stir under reduced pressure (40 mm Hg) for 30 min (at 65° C.) andsubsequently transferred to contact lens molds. The filled molds are exposed to UV light (wavelength=300-380 nm, dose=1.2-1.6 Joules/cm₂) for 20 minutes at approximately 65° C. The molds are then separated, and placed in physiological saline for 3.0 hrs at 70° C.to remove the inert diluent and any residual unreacted monomers. After thisinitial hydration period the lenses are allowed to equilibrate to room temperature in a fresh bath of physiological saline. The lenses are then tested according to Test Methods 3, 4 and 5.

The following tables display the proportions of the monomers and the results of the tests made in accordance with Test Methods 3, 4 and 5 for Examples 45-59:

    ______________________________________                                                     Example  Example   Example                                                                               Example                                              45       46        47     48                                       ______________________________________                                         Composition (%):                                                               HEMA        90.6     85.6      75.6   65.6                                     MAA         1.98     1.98      1.98   1.98                                     PEG 4000XL  5        10        20     30                                       DGBPA510    2.04     2.04      2.04   2.04                                     Darocur 1173                                                                               0.34     0.34      0.34   0.34                                     Diluent:    Phot     Phot      Phot   Phot                                                 7025     7025      7025   7025                                     Mon./Dil. Ratio                                                                            48:52    48:52     48:52  48:52                                    Properties:                                                                    Modulus (psi)                                                                              43 ± 3                                                                               44 ± 3 50 ± 2                                                                             49 ± 6                                % Elongation                                                                               133 ± 35                                                                             148 ± 34                                                                              135 ± 35                                                                           139 ± 38                              Tens. Strength                                                                              44 ± 11                                                                              46 ± 10                                                                              49 ± 9                                                                              53 ± 13                              (psi)                                                                          Water Content (%)                                                                          42 ± 1                                                                               45 ± 1 52 ± 1                                                                             56 ± 1                                Hydrogel    Clear    Clear     Clear  Clear                                    Dk          30.3     33.6      39.4   42.7                                     Kinetic Parameters:                                                            Tmax (min)  1.52     1.19      1.26   --                                       Conv. @ Tmax (%)                                                                           53.8     59.3      49.2   --                                       ______________________________________                                                     Example  Example    Example                                                                              Example                                              49       50        51     52                                       ______________________________________                                         Composition (%):                                                               HEMA        55.6     89.2      84.2   73.8                                     MAA         1.98     1.98      1.98   1.98                                     PEG 4000XL  40       5         10     20                                       DGBPA510    2.04     3.84      2.04   2.04                                     Darocur 1173                                                                               0.34     0.34      0.34   0.34                                     Diluent:    Phot     Phot      Phot   Phot                                                 7025     7025      7025   7025                                     Mon./Dil. Ratio                                                                            48:52    48:52     48:52  48:52                                    Properties:                                                                    Modulus (psi)                                                                              47 ± 7                                                                               60 ± 4 60 ± 5                                                                             62 ± 3                                % Elongation                                                                               118 ± 33                                                                              94 ± 29                                                                              126 ± 25                                                                           129 ± 33                              Tens. Strength                                                                              44 ± 12                                                                              48 ± 11                                                                               64 ± 15                                                                            64 ± 15                              (psi)                                                                          Water Content (%)                                                                          61 ± 1                                                                               37 ± 1 40 ± 1                                                                             47 ± 1                                Hydrogel    Clear    Clear     Clear  Clear                                    Dk          49.5     25.4      27.6   35.1                                     ______________________________________                                                     Example  Example   Example                                                                               Example                                              53       54        55     56                                       ______________________________________                                         Composition (%):                                                               HEMA        63.8     53.8      91.6   86.6                                     MAA         1.98     1.98      0.98   0.98                                     PEG 4000XL  30       40        5      10                                       DGBPA510    2.04     2.04      2.04   2.04                                     Darocur 1173                                                                               0.34     0.34      0.34   0.34                                     Diluent:    Phot     Phot      Phot   Phot                                                 7025     7025      7025   7025                                     Mon./Dil. Ratio                                                                            48:52    48:52     48:52  48:52                                    Properties:                                                                    Modulus (psi)                                                                              60 ± 4                                                                                52 ± 11                                                                              43 ± 3                                                                             49 ± 5                                % Elongation                                                                               109 ± 41                                                                             108 ± 27                                                                              124 ± 37                                                                           131 ± 37                              Tens. Strength                                                                              50 ± 15                                                                              52 ± 13                                                                              42 ± 9                                                                              48 ± 10                              (psi)                                                                          Water Content (%)                                                                          54 ± 2                                                                               57 ± 1 48 ± 1                                                                             52 ± 1                                Hydrogel    Clear    Clear     Clear  Clear                                    Dk          41.4     46.3      20.8   48.10                                    Kinetic Parameters:                                                            Tmax (min)  --       --        1.18   1.13                                     Conv. @ Tmax (%)                                                                           --       --        62.0   60.0                                     ______________________________________                                                     Example  Example   Example                                                     57       58        59                                              ______________________________________                                         Composition (%):                                                               HEMA        76.6     66.6      56.6                                            MAA         0.98     0.98      0.98                                            PEG 4000XL  30       30        40                                              DGBPA510    2.04     2.04      2.04                                            Darocur 1173                                                                               0.34     0.34      0.34                                            Diluent:    Phot     Phot      Phot                                                        7025     7025      7025                                            Mon./Dil. Ratio                                                                            48:52    48:52     48:52                                           Properties:                                                                    Modulus (psi)                                                                              49 ± 3                                                                               48 ± 5 46 ± 2                                       % Elongation                                                                               141 ± 35                                                                             123 ± 43                                                                              130 ± 51                                     Tens. Strength                                                                              53 ± 10                                                                              49 ± 14                                                                               52 ± 18                                     (psi)                                                                          Water Content (%)                                                                          60 ± 1                                                                               65 ± 1 70 ± 1                                       Hydrogel    Clear    Clear     Clear                                           Dk          31.1     40.2      44.0                                            Kinetic Parameters:                                                            Tmax (min)  0.89     0.82      0.68                                            Conv. @ Tmax (%)                                                                           53.4     52.7      46.4                                            ______________________________________                                    

EXAMPLES 60-69

In these examples, GLUCAM E20 was used as the diluent in conjunction with areactive monomer mixture of HEMA, MAA, PEG 4500XL (Example 3), diglycidyl bisphenol A dimethacrylate (Example 1), and Darocur 1173, in various proportions. The following is an illustrative preparation:

A reactive monomer blend made up of 5.7% by weight of the PEG 4500 cross-linker described in Example 3, 4.98% of the ethoxylated bisphenol A described in Example 1, 0.35% DAROCUR 1173, 1.98% methacrylic acid, and 87.0% HEMA was mixed with enough GLUCAM E-20 to make up a 48% monomer mix and 52% diluent. After thoroughly mixing the above blend at 65° C.,the mixture is allowed to stir under reduced pressure (40 mm Hg) for 30 min(at 65° C.) and subsequently transferred to contact lens molds. The filled molds are exposed to UV light (wavelength=300-380 nm, dose=1.2-1.6 Joules/cm₂) for 20 minutes at approximately 65° C. The molds are then separated, and placed in physiological saline for 3.0 hrs at 70° C. to remove the inert diluent and any residual unreacted monomers. After this initial hydration period the lenses are allowed to equilibrate to room temperature in a fresh bath of physiological saline. The lenses are then tested according to Test Methods 3, 4 and 5.

The following tables display the proportions of the monomers and the results of the tests made in accordance with Test Methods 3, 4 and 5 for Examples 60-69:

    __________________________________________________________________________              Example 60                                                                           Example 61                                                                           Example 62                                                                           Example 63                                                                           Example 64                                    __________________________________________________________________________     Composition (%):                                                               HEMA     87.0  81.8  73.7  59.4  48.5                                          MAA       1.98  1.98  1.98  1.98  1.98                                         PEG 4500XL                                                                              5.7   10.9  19    33.3  44.2                                          BPA890XL  4.98  4.98  4.98  4.98  4.98                                         Darocur 1173                                                                             0.35  0.35  0.35  0.35  0.35                                         Diluent: GLUCAM                                                                               GLUCAM                                                                               GLUCAM                                                                               GLUCAM                                                                               GLUCAM                                                 E20   E20   E20   E20   E20                                           Mon./Dil. Ratio                                                                         48:52 48:52 48:52 48:52 48:52                                         Properties:                                                                    Modulus (psi)                                                                           63 ± 7                                                                            63 ± 5                                                                            66 ± 4                                                                            70 ± 5                                                                            80 ± 12                                    % Elongation                                                                            119 ± 23                                                                          120 ± 33                                                                          142 ± 35                                                                          145 ± 34                                                                          159 ± 36                                   Tens. Strength                                                                          33 ± 12                                                                           34 ± 14                                                                           46 ± 18                                                                           51 ± 19                                                                           68 ± 24                                    (psi)                                                                          Water Content                                                                           56 ± 1                                                                            58 ± 1                                                                            62 ± 1                                                                            68 ± 1                                                                            71 ± 1                                     (%)                                                                            Hydrogel Clear Clear Clear Clear Clear                                         Dk       25.9  27.7  32.3  38.7  45.0                                          __________________________________________________________________________              Example 65                                                                           Example 66                                                                           Example 67                                                                           Example 68                                                                           Example 69                                    __________________________________________________________________________     Composition (%):                                                               HEMA     83.1  77.9  69.8  55.5  44.6                                          MAA       1.98  1.98  1.98  1.98  1.98                                         PEG 4500XL                                                                              5.7   10.9  19    33.3  44.2                                          BPA890XL 8.9   8.9   8.9   8.9   8.9                                           Darocur 1173                                                                             0.35  0.35  0.35  0.35  0.35                                         Diluent: GLUCAM                                                                               GLUCAM                                                                               GLUCAM                                                                               GLUCAM                                                                               GLUCAM                                                 E20   E20   E20   E20   E20                                           Mon./Dil. Ratio                                                                         48:52 48:52 48:52 48:52 48:52                                         Properties:                                                                    Modulus (psi)                                                                           86 ± 8                                                                            89 ± 4                                                                            89 ± 5                                                                            96 ± 6                                                                            102 ± 6                                    % Elongation                                                                            114 ± 14                                                                          120 ± 30                                                                          127 ± 35                                                                          163 ± 25                                                                          162 ± 25                                   Tens. Strength                                                                          40 ± 15                                                                           43 ± 19                                                                           49 ± 25                                                                           82 ± 21                                                                           87 ± 15                                    (psi)                                                                          Water Content                                                                           53 ± 1                                                                            55 ± 1                                                                            60 ± 1                                                                            65 ± 1                                                                            69 ± 2                                     (%)                                                                            Hydrogel Clear Clear Clear Clear Clear                                         Dk       21.0  23.4  29.2  34.5  40.3                                          __________________________________________________________________________

EXAMPLE 70 (Synthesis of Monocapped Polyethylene Glycol 3350) "PEG 3350MC"

A total of 200 g (0.060 mol) of dry PEG 3350 is placed into a three neck flask equipped with mechanical agitation, and a gas inlet tube. The systemis flushed with dry nitrogen and subsequently, dry oxygen. To the PEG 3350 are added 600 g of dry acetonitrile and allowed to mix until all of the PEG 3350 has completely dissolved. Subsequently, 2 drops of stannous octoate and 500 ppm of MEHQ are added. Via a dropping funnel are added 8.69 g (0.056 mol) of isocyanatoethyl methacrylate. The reaction is allowed to proceed at room temperature for 24-28 hours. The progress of the reaction is followed by the disappearance of the NCO absorption at 2270 cm⁻¹ in the infrared spectra. The acetonitrile is then removed under reduced pressure and the white waxy monocapped PEG 3350 is used as is.

EXAMPLES 71-107

In these examples, various diluents and diluent mixtures were used in conjunction with a reactive monomer mixture of HEMA, DMA, PEG 4000XL (Example 2), diglycidyl bisphenol A dimethacrylate (Example 1), PEG 3350MC(Example 70), and Darocur 1173. The following is an illustrative preparation:

A reactive monomer blend was prepared using 64.7% by weight HEMA, 20.0% N,N-dimethyl acrylamide (DMA), the dicapped PEG 4000 crosslinker describedin Example 2, 2.0% of the ethoxylated bisphenol A cross-linker described inExample 1, 6.0% of the monocapped PEG 3350 described in Example 70, and 0.34% of Darocur 1173. To 60% by weight of this monomer blend was added 40% of PEG 1000 as an inert, displaceable diluent. After thoroughly mixingthe above blend at 60° C., the mixture is allowed to stir under reduced pressure (40 mm Hg) for 30 min (at 60° C.) and subsequentlytransferred to contact lens molds. The filled molds are exposed to UV light(wavelength=300-380 nm, dose=1.2-1.6 Joules/cm₂) for 20 minutes at approximately 60° C. The molds are then separated, and placed in physiological saline for 3.0 hrs at 70° C. to remove the inert diluent and any residual unreacted monomers. After this initial hydration period the lenses are allowed to equilibrate to room temperature in a fresh bath of physiological saline. The lenses are then tested according to Test Methods 3, 4 and 5.

The following tables display the proportions of the monomers and the results of the tests made in accordance with Test Methods 3, 4 and 5 for Examples 71-107:

    __________________________________________________________________________                          Example 73                                                                           Example 74                                                                           Example 75                                                         (Modulus                                                                             (Modulus                                                                             Control                                                Example 71                                                                           Example 72                                                                           borderline)                                                                          borderline)                                                                          (Prior Art)                                                                            Example 76                                                                             Example                                                                                Example               __________________________________________________________________________                                                              78                    Composition (%):                                                               HEMA     64.7  64.7  64.7  64.7  64.7    64.7    64.7    64.7                  DMA      20    20    20    20    20      20      20      20                    PEG 4000XL                                                                              7     7     7     7     7       7       7       7                     PEG 3350MC                                                                              6     6     6     6     6       6       6       6                     BPA890XL 2     2     2     2     2       2       2       2                     Darocur 1173                                                                             0.34  0.34  0.34  0.34  0.34    0.34    0.34    0.34                 Diluent: PEG 1000                                                                             PEG 750                                                                              PEG 600                                                                              PEG 400                                                                              PEG 400BAE                                                                             GLUCAM E10                                                                             GLUCAM                                                                                 Phot 7025             Mon./Dil. Ratio                                                                         60:40 60:40 60:40 60:40 60:40   60:40   60:40   60:40                 Properties:                                                                    Modulus (psi)                                                                           25    22    19    18    51      53      51      50                    % Elongation                                                                            191   200   191   189   122     135     133     165                   Tens. Strength                                                                          27    21    24    26    46      47      44      49                    (psi)                                                                          Water Content                                                                           63.0  61.7  61.3  62.1  61.3    60.8    60.5    61.1                  (%)                                                                            Hydrogel Clear Clear Clear Clear Clear   Clear   Clear   Clear                 Kinetic                                                                        Parameters:                                                                    Tmax (min)                                                                               3.50  3.90  4.00  4.30  0.34    1.10    0.90    1.10                 Conv. at Tmax                                                                           59.0  58.0  61.0  63.0  39.0    42.0    44.0    39.0                  (%)                                                                            __________________________________________________________________________               Example 79                                                                              Example 80                                                                           Example 81                                                                              Example 82                                                                           Example 83                                                                              Example                                                                              Example                 __________________________________________________________________________                                                            85                      Composition (%):                                                               HEMA      64.7     64.7  64.7     64.7  64.7     64.7  64.7                    DMA       20       20    20       20    20       20    20                      PEG 4000XL                                                                               7        7     7        7     7        7     7                       BPA890    2        2     2        2     2        2     2                       PEG 3350MC                                                                               6        6     6        6     6        6     6                       Darocur 1173                                                                              0.34     0.34  0.34     0.34  0.34     0.34  0.34                   Diluent (%):                                                                   PEG 400   90       75    60       50    35       25    15                      Photonol 7025                                                                            10       25    40       50    65       75    85                      Mon./Dil. Ratio                                                                          60:40    60:40 60:40    60:40 60:40    60:40 60:40                   Properties:                                                                    Modulus (psi)                                                                            27       31    30       39    42       51    52                      % Elongation                                                                             200      210   190      186   175      185   160                     Tens. Strength (psi)                                                                     28       31    29       35    40       40    43                      Water Content (%)                                                                        62.1     61.9  62.0     61.2  61.1     60.9  60.7                    Hydrogel  Clear    Clear Clear    Clear Clear    Clear Clear                   Kinetic Parameters:                                                            Tmax (min)                                                                               4.2      4.0   3.9      3.4   2.1      1.6   1.2                     Conv. @ Tmax (%)                                                                         59.0     56.0  52       53    51.0     48.0  41.0                    __________________________________________________________________________               Example 86                                                                              Example 87                                                                           Example 88                                                                              Example 89                                                                           Example 90                                                                              Example                                                                              Example                 __________________________________________________________________________                                                            92                      Composition (%):                                                               HEMA      64.7     64.7  64.7     64.7  64.7     64.7  64.7                    DMA       20       20    20       20    20       20    20                      PEG 4000XL                                                                               7        7     7        7     7        7     7                       BPA890    2        2     2        2     2        2     2                       PEG 3350MC                                                                               6        6     6        6     6        6     6                       Darocur 1173                                                                              0.34     0.34  0.34     0.34  0.34     0.34  0.34                   Diluent (%):                                                                   PEG 400   90       75    60       50    90       75    60                      GLUCAM E20                                                                               10       25    40       50    10       25    40                      Mon./Dil. Ratio                                                                          60:40    60:40 60:40    60:40 60:40    60:40 60:40                   Properties:                                                                    Modulus (psi)                                                                            24       29    30       37    44       48    52                      % Elongation                                                                             185      190   188      178   150      150   141                     Tens. Strength (psi)                                                                     25       29    31       34    41       39    45                      Water Content (%)                                                                        61.8     61.7  61.2     61.0  60.8     60.7  60.5                    Hydrogel  Clear    Clear Clear    Clear Clear    Clear Clear                   Kinetic Parameters:                                                            Tmax (min)                                                                               4.1      3.7   3.2      2.1   1.4      1.0   0.9                     Conv. @ Tmax (%)                                                                         59.0     50.0  49.0     46.0  48.0     44.0  47.0                    __________________________________________________________________________                      Example 94                                                                     (Modulus                                                                Example 93                                                                            borderline)                                                                          Example 95                                                                            Example 96                                                                           Example 97                                                                            Example 98                                                                           Example                                                                              Examp.100               __________________________________________________________________________     Composition (%):                                                               HEMA      64.7   64.7  64.7   64.7  64.7   64.7  64.7  64.7                    DMA       20     20    20     20    20     20    20    20                      PEG 4000XL                                                                               7      7     7      7     7      7     7     7                       BPA890    2      2     2      2     2      2     2     2                       PEG 3350MC                                                                               6      6     6      6     6      6     6     6                       Darocur 1173                                                                              0.34   0.34  0.34   0.34  0.34   0.34  0.34  0.34                   Diluent (%):                                                                   PEG 1000  100    90    75     60    50     35    25    15                      GLUCAM E20                                                                               0      10    25     40    50     65    75    85                      Mon./Dil. Ratio                                                                          60:40  60:40 60:40  60:40 60:40  60:40 60:40 60:40                   Properties:                                                                    Modulus (psi)                                                                            25     21    28     33    34     33    47    49                      % Elongation                                                                             191    190   175    184   141    132   122   111                     Tens. Strength (psi)                                                                     27     30    37     31    42     41    49    41                      Water Content (%)                                                                        63.0   62.3  62.0   61.6  61.0   61.3  60.8  61.0                    Hydrogel  Clear  Clear Clear  Clear Clear  Clear Clear Clear                   Kinetic Parameters:                                                            Tmax (min)                                                                               3.5    3.3   2.9    2.6   2.1    1.4   1.1   1.1                     Conv. @ Tmax (%)                                                                         59.0   55.0  53.0   54.0  49.0   47.0  46.0  41.0                    __________________________________________________________________________               Examp. 101                                                                     (Modulus                                                                       borderline)                                                                             Examp. 102                                                                           Examp. 103                                                                              Examp. 104                                                                           Examp. 105                                                                              Examp.                                                                               Examp.                  __________________________________________________________________________                                                            107                     Composition (%):                                                               HEMA      64.7     64.7  64.7     64.7  64.7     64.7  64.7                    DMA       20       20    20       20    20       20    20                      PEG 4000XL                                                                               7        7     7        7     7        7     7                       BPA890    2        2     2        2     2        2     2                       PEG 3350MC                                                                               6        6     6        6     6        6     6                       Darocur 1173                                                                              0.34     0.34  0.34     0.34  0.34      0.34                                                                                0.34                   Diluent (%):                                                                   PEG 1000  90       75    60       50    90       75    60                      Photonol 7025                                                                            10       25    40       50    10       25    40                      Mon./Dil. Ratio                                                                          60:40    60:40 60:40    60:40 60:40    60:40 60:40                   Properties:                                                                    Modulus (psi)                                                                            19       27    32       35    39       45    46                      % Elongation                                                                             183      175   181      177   131      125   130                     Tens. Strength (psi)                                                                     36       28    31       33    41       41    47                      Water Content (%)                                                                        61.1     62.8  62.5     62.1  61.5     60.7  60.8                    Hydrogel  Clear    Clear Clear    Clear Clear    Clear Clear                   Kinetic Parameters:                                                            Tmax (min)                                                                               3.6      3.4   3.1      2.7   1.4      1.1   1.1                     Conv. @ Tmax (%)                                                                         49.0     51.0  45.0     39.0  41.0     42.0  44.0                    __________________________________________________________________________

EXAMPLE 108 Synthesis of Isocyanatoethyl Methacrylate Capped PEG 2000 Monomethyl Ether

A total of 200 g (0.10 mol) of dry PEG 2000 monomethyl ether is charged into a 1 L three neck flask equipped with a mechanical stirrer and a gas inlet tube. A total of 600 g of dry acetonitrile is added to the flask, and the monomethoxy PEG 2000 allowed to dissolve completely. The system isthen flushed with dry nitrogen and then dry oxygen. Subsequently, two dropsof stannous octoate and 500 ppm of 4-methoxy hydroquinone (MEHQ) is added to the flask. Using a dropping funnel 15.51 g (0.10 mol) of isocyanatoethyl methacrylate in 50 g of acetonitrile are added dropwise tothe contents of the 1 L flask. The reaction is allowed to proceed at room temperature for 24-28 hrs. The progress of the reaction is followed by monitoring the disappearance of the NCO absorption at 2270 cm⁻¹ in the infrared spectrum. After the reaction is deemed complete (no absorption at 2270⁻¹), the solvent is removed under reduced pressure and the white, waxy monocapped monomethoxy PEG 2000 is used as is.

EXAMPLES 109-120

A reactive monomer blend was prepared using various amounts of HEMA, 20.0% N,N-dimethyl acrylamide (DMA), 16.0% of the dicapped PEG 4500 crosslinker described in Example 3 (PEG 4500XL), 8.0% of the ethoxylated bisphenol A crosslinker described in Example 1 (BPA890), various amounts of the monocapped monomethoxy PEG 2000 described in Example 108 (MC mPEG 2000), and 0.4% of Darocur 1173. To 55% by weight of this monomer blend was added45% of an inert, displaceable diluent made up of 50% GLUCAM E-20 and 50% Photonol 7025. After thoroughly mixing the above blend at 60° C., the mixture is allowed to stir under reduced pressure (40 mm Hg) for 30 min (at 60° C.) and subsequently transferred to contact lens molds.The filled molds are exposed to UV light (wavelength=300-380 nm, dose =1.2-1.6 Joules/cm₂) for 20 minutes at approximately 60° C. The molds are then separated, and placed in physiological saline for 3.0 hrs at 70° C. to remove the inert diluent and any residual, unreacted monomers. After this initial hydration period the lenses are allowed to equilibrate to room temperature in a fresh bath of physiological saline. The lenses are then tested according to Test Methods3, 4 and 5.

The reactive monomer mixture formulations and the results of the tests of the lenses prepared in accordance with Examples 109-120 are shown in the following tables:

    __________________________________________________________________________               Examp. 109                                                                           Examp. 110                                                                           Examp. 111                                                                           Examp. 112                                                                           Examp. 113                                                                           Examp. 114                             __________________________________________________________________________     Composition (%):                                                               HEMA      43.6  34.6  20.6  43.6  34.6  20.6                                   DMA       20    20    20    20    20    20                                     PEG 4500XL                                                                               16    16    16    16    16    16                                     BPA890    8     8     8     8     8     8                                      MC mPEG 2000                                                                             12    21    35    12    21    35                                     Darocur 1173                                                                             0.4   0.4   0.4   0.4   0.4   0.4                                    Diluent (%):                                                                   Photonol 7025                                                                            50    50    50    50    50    50                                     GLUCAM E-20                                                                              50    50    50    50    50    50                                     Mon./Dil. Ratio                                                                          55:45 55:45 55:45 45:55 45:55 45:55                                  Properties:                                                                    Modulus (psi)                                                                            76    77    75    51    44    47                                     % Elongation                                                                             148   113   117   142   119   128                                    Dk        37    42    50    40    47    55                                     Water Content (%)                                                                        70.5  73.8  78.1  72.9  76.6  80.3                                   Hydrogel  Clear Clear Clear Clear Clear Clear                                  __________________________________________________________________________               Examp. 115                                                                           Examp. 116                                                                           Examp. 117                                                                           Examp. 118                                                                           Examp. 119                                                                           Examp. 120                             __________________________________________________________________________     Composition (%)                                                                HEMA      36.6  27.6  13.6  36.6  27.6  13.6                                   DMA       20    20    20    20    20    20                                     PEG 4500XL                                                                               16    16    16    16    16    16                                     BPA890    15    15    15    15    15    15                                     MC mPEG 2000                                                                             12    21    35    12    21    35                                     Darocur 1173                                                                             0.4   0.4   0.4   0.4   0.4   0.4                                    Diluent (%):                                                                   Photonol 7025                                                                            50    50    50    50    50    50                                     GLUCAM E-20                                                                              50    50    50    50    50    50                                     Mon./Dil. Ratio                                                                          55:45 55:45 55:45 45:55 45:55 45:55                                  Properties:                                                                    Modulus (psi)                                                                            130   126   125   87    90    85                                     % Elongation                                                                             96    81    68    122   90    78                                     Dk        29    33    50    40    47    55                                     Water Content (%)                                                                        64.7  68.2  78.1  72.9  76.6  80.3                                   Hydrogel  Clear Clear Clear Clear Clear Clear                                  __________________________________________________________________________ 

What is claimed is:
 1. A process for producing shaped hydrogel articles which comprises the steps of:(1) molding or casting a polymerization mixture comprising:(a) a monomer mixture comprising a major proportion of one or more hydrophilic monomers, and one or more crosslinking monomers; and (b) an inert, displaceable, non-aqueous diluent comprising an ethoxylated C₃₋₆ alkanetriol;under conditions to polymerize said monomer mixture to produce a shaped gel of a copolymer of said monomers and said diluent; and (2) thereafter replacing said diluent with water, provided that said inert, displaceable, non-aqueous diluent is selected such that when said polymerization mixture is polymerized in a photo differential scanning calorimeter wherein said polymerization is induced by ultraviolet irradiation at a light intensity of from about 2.5 to 3 mW/cm², the time to maximum exotherm of said polymerization is within the range of from about 0.2 to about 3.5 minutes and the percent conversion to polymer of the monomer mixture at maximum exotherm is at least 40 percent. 